ESITO VII

European Symposium for

Insect Taste and Olfaction

 

Posters
Talks
Schedule
ESITO Homepage


1

Alessandro Desogus 1, Bill S. Hansson 2 and Anna Maria Angioy 1

1 Department of Experimental Biology
University of Cagliari, I 09042 Monserrato-Cagliari, Italy
2 Department of Ecology Lund University, SE-223 62 Lund, Sweden
[email protected], [email protected], [email protected]

Functional analysis of olfactory sensitivity to sex pheromone and plant-associated odours in males and females of Spodoptera littoralis moths

Olfactory information plays a fundamental role in driving behavioural responses in insects. Moreover, odour reception induces cardiac responses that have been described as a sensitive test of insect reactivity to sensory stimulation.

The female of Spodoptera littoralis moths produces a male-attracting sex pheromone blend eliciting search behaviour in males. Both sexes possess antennal olfactory receptor neurons and antennal lobe neurons responding specifically and sensitively to the blend as well as to single sex pheromone components. However, the behavioural role of pheromone autodetection in the females is unknown.

Cotton is a preferred host plant of S. littoralis. Perception of volatiles such as odours associated with an intact cotton plant, or induced in response to herbivory, as well as flower odours and green leaf volatiles, also elicits behavioural responses in S. littoralis moths. Receptor neurons responding with high specificity to plant odours and antennal lobe interneurons with high specificity to several plant compounds were found in both sexes.

In the present study we have used a trial procedure to test the effects of several olfactory stimuli on the heart activity of S. littoralis moths of both sexes. By recording electrocardiograms from intact male and female specimens, we characterised the heart response to single female-produced sex pheromone components, to the male-attracting blend and to plant odours such as geraniol, ± linalool and indol. Response threshold and latency were determined. Chemicals were tested at concentrations ranging between (1x10-5) fg and 10µg loaded onto a filter paper. Pure air and hexane were used for control and blank stimulation respectively. All measurements were repeated in a triplicate series of experiments performed on three different groups of specimens.

In both sexes, stimulation with each test odour was followed by cardiac responses after 0.9-1.0 s latency. Extremely low concentrations were needed to elicit a response. The lowest response threshold (1x10-4fg) was established for the complete pheromone blend as well as for the major blend component when tested on males. A higher threshold value (1x10-2fg) was measured following stimulation with the minor blend component. In females, the pheromone blend threshold was in turn several hundred times higher than that measured in males, as well as much higher than that obtained in females stimulated with a biologically meaningful plant odour such as geraniol.

Besides showing the high sensitivity of cardiac responses to odour information in insects, results stress the physiological importance of sex pheromone detection for female Spodoptera moths pointing to the need for future behavioural studies. Supported by: Socrates-EU Grant; Italian Ministry of University and Scientific Research; Swedish Natural Sciences Research Council.

 


2

Sylvia Anton and Rickard Ignell

Department of Ecology
Lund University, S-223 62 Lund, Sweden
[email protected]

Developmental changes in the structure and function of the central olfactory system in desert locusts

Desert locusts are guided by olfactory cues in different behavioural contexts. The behavioural response to the same olfactory stimuli changes during development and with the physiological state of these hemimetabolous insects. Nymphs e.g. communicate using different aggregation pheromones than adult locusts. We have studied the neurobiological basis for such behavioural changes using neuroanatomical and intracellular recording techniques.

From previous studies we know that the number of olfactory sensilla on the antennae increases during development (Ochieng¹ et al. 1998). The olfactory receptor neurons (ORNs) housed in these sensilla send their axons into the antennal lobe (AL), the primary olfactory neuropil, where they make synaptic contact with local interneurons and projection neurons (PNs). The number of glomeruli within the AL increases significantly between 1st instar nymphal and adult locusts. ORNs and AL PNs have multiglomerular arborisations within the AL. A constant number of PNs innervates an increasing number of glomeruli with each developmental stage. During development, the percentage of neurons responding specifically to single aggregation pheromone components decreases, whereas the percentage of neurons with broader response spectra increases. The percentage of neurons responding to green leaf volatiles, however, remains constant. Although ORNs and PNs responding to all aggregation pheromone components and blends are found in both nymphs and adults, the proportion of PNs responding to stage-specific components or blends is much higher than of those responding to components or blends produced by other stages.

Our data show that anatomical and physiological properties of the AL and its neurons to a large extent reflect the changes in olfactory guided behaviour during development. Increasing convergence of ORNs onto a constant number of PNs contributes to changes in the central integration of odours during development.

Reference:

Ochieng¹ SA, Hallberg E, Hansson BS (1998) Fine structure and distribution of antennal sensilla of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae). Cell Tissue Res 291:525-536

Supported by Swedish Research Councils (NFR, SAREC).

 


3

M. A. Carlsson and B. S. Hansson

Department of Ecology Lund University S-223 62 Lund, Sweden
[email protected]

Odour maps in the fly brain

We optically measured calcium changes in the antennal lobes of the fly Protophormia terranovae upon stimulation with biologically relevant odorants. In accordance with studies in other insect species different odorants evoked unique but often overlapping patterns of glomerular activity.

P. terranovae is an important pollinator of the plant Helicodiceros muscivorous (Stensmyr et al., this conference). The plant mimics the odour of carcasses, which attracts gravid female. Headspace samples from H. muscivorous and rotten meat evoked similar activity patterns in the antennal lobes. Both of these multimolecular odours evoked distributed activity patterns with several active glomeruli. Several of the monomolecular substances emitted from either rotten meat or H. muscivorous showed more restricted activity patterns than the extracts.

We further found that activity patterns were roughly bilaterally symmetrical between the lobes. The relative positions of activated glomeruli were conserved between individuals indicating a spatial olfactory code.

 


4

M. A. Carlsson1, B. Kalinova1,2 and B. S. Hansson1

1 Department of Ecology,Lund University
S-223 62 Lund, Sweden
[email protected]

2 Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic
Flemingovo nám. 166 10 Praha 6

Glomerular responses to sexual pheromones and plant-related odorants in male and female sphinx moth, Manduca sexta

We have investigated the glomerular representation of odorants in male and female sphinx moth, Manduca sexta. Optical recordings were used to study intracellular changes in Ca2+ concentration. A large part of the calcium signals are believed to reflect presynaptic activity in the terminals of sensory neurons. Therefore, patterns of glomerular activity seen in the recordings should represent the types of receptor neurons involved in detection of an odorant.

In male moths a large glomerulus situated close to the entrance of the antennal nerve was activated by the minor pheromone component, E10,E12,Z12-hexadecatrienal. The position of this glomerulus corresponds to the identified compartment of the macroglomerular complex, MGC, called the cumulus. The major pheromone component, E10,Z12-hexadecadienal or bombykal, activated a glomerulus located more medial than the former at a position corresponding with the toroid subdivision of the MGC. Earlier studies have shown that projection neurons responding to the minor and major pheromone component arborise in the cumulus and the toroid, respectively (Hansson et al., 1991). Thus, there seems to be a matching of input and output signals.

Very few data are available concerning processing of plant-related odorants in ordinary glomeruli. We used monomolecular plant odorants from different chemical classes (Shields and Hildebrand, 2001; Kalinova and Hansson, this conference). All odorants evoked distributed patterns of glomerular activity. Different odorants often showed overlapping, however unique, activity patterns suggesting that information regarding odorants sharing a certain molecular feature is transmitted through a common channel.

Glomerular responses to plant odorants were similar between individuals of both sexes. Responses were also roughly bilaterally symmetrical between the lobes. Our results indicate that a spatial olfactory code exists, as has been demonstrated in the honeybee (Galizia et al., 1999).

Responses to plant odorants were restricted to the ordinary glomeruli and pheromone components mainly to the MGC. Different coding strategies are evident in the two olfactory subsystems. Input to the MGC comes from highly specific sensory neurons tuned to a specific component. In contrast, plant odorants are detected by less specifically tuned neurons (probably specific to a certain molecular determinant). Thus, to discriminate between different plant odorants, responses in several types of neurons must be compared in an across-neuron (and hence across-glomerular) fashion.

References:

Galizia, G.G.; Sachse, S.; Rappert, A.; Menzel, R. (1999a). The glomerular code for odor representation is species specific in the honeybee Apis mellifera. Nat. Neurosci. 2(5), 473-478.

Hansson, B.S.; Christensen, T.A.; Hildebrand, J.G. (1991). Functionally distinct subdivisions of the macroglomerular complex in the antennal lobe of the male sphinx moth Manduca sexta. J. Comp. Neurol. 312, 264-278.

Shields, V.D.C. And Hildebrand, J. G. Responses of a population of antennal olfactory receptor cells in the female moth Manduca sexta to plant-associated volatile organic compounds. J. Comp. Physiol. A. 186, 1135-1151.

 


5

Holly Cate and Charles Derby

Department of Biology
Georgia State University Atlanta, Georgia USA
[email protected], [email protected]

Parallel antennular chemosensory pathways for olfactory behaviors in lobsters: structure and function of chemosensilla

In this study, we describe the structure and function of receptors that mediate olfactory behavior in lobsters. The antennules are the primary olfactory organ of decapod crustaceans. Antennules contain thousands of chemosensilla, which are cuticular extensions of the exoskeleton that are innervated by dendrites of chemosensory neurons and. To date, most studies on chemoreception in decapods have focused on the prominent aesthetasc sensilla, which are innervated by chemosensory neurons that project to the glomerular olfactory lobes (3). Recent behavioral studies suggest that a lobster's capacity to perform olfactory mediated tasks, such as odor localization, learning, and discrimination, is only marginally diminished following aesthetasc ablation (1,4).

Thus, non-aesthetasc chemosensilla appear to be sufficient for mediating olfactory behaviors. Yet very little is known about these non-aesthetasc sensilla, even their identity. Using scanning electron microscopy, we have determined that there are 10 morphological types of setae on the antennular flagella, including the aesthetascs. The most abundant and widely distributed of the non-aesthetascs are the hooded sensilla. Using scanning and transmission electron microscopy and electrophysiology, we determined that hooded sensilla are bimodal (chemo- and mechanoreceptive) and are present on virtually all segments of the antennules. Each hooded sensillum is innervated by 9-10 chemosensory neurons and 3 mechanosensory neurons. Their chemosensory neurons respond to waterborne chemicals and have different response specificities. Their mechanosensory neurons have relatively high thresholds, responding only to tactile stimulation. Hooded sensilla are phylogenetically widely distributed, being present on all examined representatives of all three families of lobsters. Chemosensory neurons innervating non-aesthetasc sensilla project to the non-glomerular lateral antennular neuropils (2). Thus, hooded sensilla are expected to mediate antennular chemoreception through the lateral antennular neuropil pathway that parallels the aesthetasc/olfactory lobe pathway.

Supported by NSF IBN 0077474 and NIH DC00312

References:

1. Horner A.J., Ngo V., Steullet P., Keller T., Weissburg M., and Derby C.D.. 2000. The role of different types of antennular sensilla in orientation by Caribbean spiny lobsters to natural odor stimuli under controlled flow conditions. Chem. Senses 25: 670-671.

2. Schmidt M., Van Ekeris L., and Ache B.W. 1992. Antennular projections to the midbrain of the spiny lobster. I. Sensory innervation of the lateral and medial antennular neuropils. J. Comp. Neurol. 318: 277-290.

3. Schmidt M. and Ache B.W. 1992. Antennular projections to the midbrain of the spiny lobster. II. Sensory innervation of the olfactory lobe. J. Comp. Neurol. 318: 291-303.

4. Steullet, P., Kruetzfeldt D., Hamidani G., Flavus T., and Derby C.D. 2000. Functional overlap of two antennular chemosensory pathways in food odor discrimination behavior of spiny lobsters. Chem. Senses 25: 671.

 


6

M. Eugenia Chiappe and Leslie B. Vosshall

The Rockefeller University
1230 York Avenue
New York, NY 10021 USA
[email protected]

A Broadly Expressed Odorant Receptor Gene in Drosophila

Drosophila melanogaster possesses two main olfactory organs: the third antennal segment and the maxillary palps. Approximately 1200 and 120 Drosophila odorant receptor neurons (ORNs) are present in the antenna and the maxillary palps, respectively. ORNs express odor-binding receptors in their dendrites located at the shaft of the sensory sensilla. Previous work in our laboratory and others identified 61 Drosophila odorant-receptor (DOR) genes, of which 42 display topographically restricted expression in a subset of neurons in either the antenna or the maxillary palp. All neurons expressing a given odorant receptor gene extend axons that converge upon one or two glomeruli in the insect¹s antennal lobe (AL). These canonical DORs are thought to confer upon neurons specific responses to a unique set of odorous ligands. In contrast, Or83b encodes a second type -non-canonical- receptor: Or83b is broadly expressed in both the maxillary palps and the antenna. We have analyzed the overlap of expression between Or83b and the canonical DORs. While the maxillary palp ORNs co-express Or83b with the canonical palp-DOR genes, the antenna shows a more complex organization: some ORNs co-express Or83b with the antennal-DOR gene, whereas others only express the canonical receptors. These results were confirmed by the analysis of the ORN projections in the AL. We are interested in the function that this non-canonical receptor may play in the logic of olfactory processing in the insect. Interestingly, similarly broad expression has been observed for two goldfish odorant receptors, and for a mouse vomeronasal receptor, suggesting that these non-canonical receptors may be involved in modulating the ORN¹s responsiveness to odorants.

 


7

Nicolas Meunier, Frédéric Marion-Poll

INRA Station de Phytopharmacie et Médiateurs Chimiques
78026 Versailles Cedex, France
[email protected]

How sensitive is the water cell in Drosophila taste sensilla?

Insect taste neurons are grouped into individual hairs called sensilla. In most insects, one taste neuron is said to respond to water and to be inhibited by the osmotic pressure. We are currently reexamining its sensitivity in adult Drosophila melanogaster taste hairs of the front legs. In these hairs, the water cell (W) and the sugar cell (S) are both active when stimulated with sugars like 10-1 to 10-2 M saccharose. To get a correct picture of the activity of both neurons stimulated with various concentrations of sugars, we need to separate their firing activity with a good accuracy.

On principle, this operation is simple. In D. melanogaster, the W cell consistently elicits large spikes and the S cell elicits smaller spikes. Several computer programs were tailored to separate spike trains using classification and sorting algorithms.They perform reasonably well, unless several neurons are active simultaneously. Usually, it is considered that if two neurons fire at almost the same time, the resulting waveform is a simple addition of the two waveforms. Otherwise, the spike amplitudes should remain stable.

We observed that the amplitude of W spikes is reduced in proportion to its temporal distance from S spikes. These changes of amplitude make former sorting algorithms inoperative, and lead to underestimate the activity of the W cell. We propose to analyze such records using interactive sorting tools, taking into account the temporal regularity of the firing from both cells.

References:

1 Stitt J.P., Gaumond R.P., Frazier J.L., Hanson F.E. (1998) Action potential classifiers: a functional comparison of template matching, principal components analysis and an artificial network. Chem. Senses 23: 531-539

2 Schnuch M., Hansen K. (1990) Sugar sensitivity of a labellar salt receptor of the blowfly Protophormia terraenovae. J. Insect Physiol. 36: 409-407.

 


8

A.L. Carbajal de la Fuente and S.S. Catalá

CRILAR (Centro Regional de Investigaciones La Rioja)
Anillaco, La Rioja 5301, Argentina.
[email protected]

Relationship between antenna sensillar pattern in six species of Triatominae (Hemiptera: Reduviidae) and the habitats in which they develop.

Chagas disease is transmitted by triatomine bugs, the main disease transmitted by an insect vector in Latin America. Triatomines are haematophagous during all life stage and there are some 129 species in Central and South America. These insects use their antennal sensilla when searching for vertebrate hosts, refuge and mates. The number of each sensilla type and their distribution on the antenna of six triatomine species from two different biogeographical zones of Brazil were analyzed. The hypothesis is that triatomines from these distinct regions show a common form in their antennal sensorial system as they live in similar habitats in both regions. The number and distribution of mechanoreceptive bristles, and thin walled trichoidea, thick walled trichoidea and basiconica were studied. The species studied were: Triatoma infestans (Cerrado Region) and T. brasiliensis (Caatinga Region) frequently occurring in the home, T. sordida (Cerrado Region) and T. pseudomaculata (Caatinga Region) that colonize peridomestic habitats, and Rhodnius neglectus (Cerrado Region) and R. nasutus (Caatinga Region) that inhabit palms. Antennae of 60 insects were examined, 10 from each species (5 males and 5 females) after clearing in 5% NaOH and neutralized with acetic acid. The observations were carried out on antennae mounted in glycerine, using an optical microscopy with clear camera (400x).

The results showed significant differences for both type and number of sensilla in the six species, as well as in the presence or absence of certain types of sensilla on the pedicel. There were significant sexual differences between T. sordida, T. brasiliensis and T. pseudomaculata. Multivariate analysis showed a separation of the two species that live in palms from the species belonging to the domestic and peridomestic habitats. However, some species converged at the center, where T. infestans is present. The results indicate that the patterns of antennal sensilla are sensitive indicators of adaptative processes in the evolution of triatomines, and they support the idea that those species that frequent less stable habitats or a larger variety of habitats possess more types on the pedicel and higher sensilla numbers. On the other hand, species that colonize stable habitats posses a more simplified sensillar pattern.

This work was funded by the ECLAT network , with EU and Avina Foundation funds.

 


9

Joseph C. Dickens, James E. Oliver, Benedict Hollister and Jerome A. Klun

U. S. Department of Agriculture
Henry A. Wallace Beltsville Agricultural Research Center, Plant Sciences Institute
Chemicals Affecting Insect Behavior Laboratory, Beltsville, MD 20705
[email protected]

Chemical Signals in the Colorado Potato Beetle

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Coleoptera: Chrysomelidae), is a major pest of potatoes where they are grown. The nature of chemically mediated behavior of CPB and the identification of specific chemicals responsible for it have long been investigated by numerous researchers throughout the world. Recently, we identified a number of synthetic blends of plant volatiles that attract CPB in both laboratory bioassays and field tests. Now we have discovered other volatile chemicals produced by CPB that modify behavior of conspecifics. We will discuss how these chemicals were discovered, how they regulate behavior, and neural mechanisms involved in their detection. Based on the studies presented here and other recent results, a model was developed to account for host plant selection and reproduction in CPB.

 


10

Galizia C. Giovanni, Bernd Kimmerle, Randolf Menzel

Institut fur Neurobiologie
FU Berlin, Konigin-Luise-Str. 28/30
14195 Berlin
[email protected]

Local interneurons in the honeybee antennal lobe: physiological and morphological analysis combining electrophysiology, optical imaging and confocal microscopy

In insects, the first brain structure to process olfactory information is the antennal lobe (AL). It is subdivided into 160 olfactory glomeruli which receive input from the olfactory receptor neurons. Projection neurons connect the AL to higher order brain centres. Within the honeybee AL, ca. 4000 local interneurons (LNs) interconnect the olfactory glomeruli. Electrophysiological responses of these neurons have been described previously. Here we have combined intracellular recordings with (successive) calcium imaging of the impaled cell, followed by confocal reconstruction of its morphology. Therefore, we can describe both the temporal response properties (in terms of spike trains and intracellular Calcium dynamics) and the spatial response patterns (in terms of activated glomeruli). Electrophysiological recordings generally showed a continuous background activity consisting of spikes of diverse shape and amplitude. Using a spike-sorting algorithm we show that responses to odours can consist of a decrease in the rate of one spike type, and/or an increase in the rate of a different spike type. Some responses temporally matched the stimulus length, i.e. stopped with stimulus offset, others persisted after the stimulus had ended. Calcium imaging showed that the diverse spike shapes corresponded to responses in individual and distinct glomeruli. An odour-response consisting of a decrease in one spike type and increase in another led to a calcium decrease in one glomerulus and an increase in another. Different odours elicited different response patterns, which again were matched between the electrophysiology and the calcium imaging. The confocal reconstructions showed that we have recorded from heterogeneous LINs, i.e. neurons that innervate one glomerulus densly, and the rest of the AL sparsly. In some cases the densly innervated glomerulus could be morphologically identified in an atlas of the olfactory lobe. Generally, more than one soma was labelled, and more than one glomerulus was densly innervated. We conclude that LINs are electrically coupled. Alternatively, LINs may have several spike initiating zones, with each initiating zone being associated to a given glomerulus.

 


11

Birgit Greiner, Christophe Gadenne and Sylvia Anton

Department of Ecology, Sölvegatan 37
Lund, Sweden
[email protected]

Age-independent central nervous processing of plant volatiles in Agrotis ipsilon males showing age-dependent processing of sex pheromone

Male moths rely on female sex pheromones to find their mating partner and on plant volatiles mainly for food sources. In the noctuid moth, Agrotis ipsilon, central nervous processing of sex pheromone in the macroglomerular complex of the antennal lobe (AL) is age- and juvenile-hormone-dependent. The sensitivity of AL interneurons to the sex pheromone increases with age and juvenile-hormone-level. We investigated whether age could affect not only central sex pheromone processing, but also the central nervous processing of plant volatiles in the plant-specific ordinary glomeruli of A. ipsilon males. Intracellular recordings of AL interneurons were performed in males of different ages after stimulation of the antennae with 7 different plant volatiles, including heptanal a behaviourally active volatile for A. ipsilon. Responses to all tested compounds were found, but most frequently to heptanal and (E)-2-hexenal. There was no difference in sensitivity of the AL interneurons for any of the plant volatiles tested between newly emerged non mature and fully sexually mature males. Moreover, the specificity of AL neurons for any plant volatile did not differ with age. From these results we conclude that the sensitivity of the antennal lobe neurons involved in central processing of plant volatiles is age-independent. Thus, juvenile hormone, is most likely only involved in the modulation of sex pheromone processing and not in plant volatile processing in A. ipsilon.

Supported by Swedish Research Councils (NFR, SJFR) and the Swedish Institute.

 


12

Jocelijn Meijerink, Mikael Carlsson & Bill S. Hansson

Department of Ecology
Lund University
Sölvegatan 37 SE-22362 Lund, Sweden
[email protected]

Olfactory coding in the moth antennal lobe: aspects of chain length

In order to study spatial coding of odours within the antennal lobe of the moth Spodoptera littoralis optical imaging studies were performed. Odour evoked activation patterns in the antennal lobe were investigated in response to series of primary aliphatic alcohols and aldehydes each ranging in carbon atom number from C5-C12 (n=18). Several of these odours are known hostplant volatiles for Spodoptera littoralis. Activation patterns were studied in response to amounts of odours around threshold level. The amount of compound applied to the filter paper was adjusted to correct for differences in volatility. In this way the amount of odour reaching the moths antennae was assumed to be equal for each tested odour within a chemical group.

Preliminary analysis of the data showed that activity patterns are correlated with the chain length of the molecule. These findings correspond with studies in Apis mellifera (Sachse et al., 1999). Short chain length aldehydes and alcohols (C5, C6) evoked activation in the ventral medial part of the antennal lobe. With increasing chain length the activation pattern was gradually shifting to the dorsal lateral part of the lobe. Alcohols and aldehydes with chain lengths of nine carbon atoms or more elicited only activation in the dorsal lateral part of the lobe.

At threshold levels nonanal and heptanol evoked activity in a larger area of the antennal lobe compared to some of the other compounds, which activated an area corresponding to the size of one glomerulus. These data might indicate that there are more ORNs responding to nonanal and heptanol compared to the other odours. Threshold values for all odours were in the same order of magnitude as thresholds determined in single sensillum studies on female Spodoptera littoralis (Anderson et al., 1995). Only activity patterns elicited at threshold level will reveal functional specificity of glomeruli.

Supported through a European Community Marie Curie Fellowship & Stiftelsen Wenner-Grenska Samfundet

References:

1. Anderson et al. (1995). Physiol. Entomol. 20: 189-198

2. Sachse et al. (1999). Eur. J. Neurosci. 11: 3970-3982

 


13

Amy Horner , Pascal Steullet and Charles Derby

Department of Biology
Georgia State University Atlanta, Georgia USA
[email protected]

The role of different types of antennular sensilla in orientation by Caribbean spiny lobsters to natural odor stimuli

The ability of Caribbean spiny lobsters to detect and orient to specific chemical stimuli in the environment is essential for a variety of behaviors including the localization of potential prey, shelter, and mates. Although chemoreceptive elements can be found on most body surfaces, the major olfactory organ of the spiny lobster consists of the paired antennules. Each antennule bifurcates into a lateral and medial flagellum that house a diversity of sensilla. The most prominent chemosensory sensilla are the aesthetascs on the lateral flagella, but there are several additional populations of non-aesthetasc chemosensory sensilla distributed throughout the antennules(1). The receptor neurons associated with the aesthetasc and non-aesthetasc chemosensilla project to the central nervous system in two parallel pathways (2,3). Aesthetasc chemoreceptor neurons project to the olfactory lobes, whereas non-aesthetasc chemoreceptor neurons project to the lateral antennular neuropils. How these two pathways function separately and in concert to drive chemically mediated behaviors is unclear. The aim of this study was to examine the function of these sensillar pathways during orientation to a distant food odor stimulus. To generate naturalistic flow conditions, all trials were conducted in an 8,000-liter flume with a flow rate of 5-cm/ sec and low turbulence. To test the relative importance of aesthetascs and non-aesthetascs for orientation, we selectively ablated each sensillar population and compared the ability of ablated animals to locate an odor source to that of intact animals. Lobsters were released into the flume 2 m downstream from the stimulus source and were allowed to move freely. All trials were videotaped from above, and the two dimensional paths taken by the lobsters were analyzed using motion analysis software. Animals with both aesthetasc and non-aesthetasc sensilla ablated rarely located the odor source. In contrast animals with either aesthetasc or non-aesthetasc sensilla ablated frequently located the stimulus source, though they tended to take slightly longer and more convoluted paths than completely intact animals. These results suggest that either chemosensory pathway is sufficient to drive orientation behavior, and that there is substantial overlap in the roles of aesthetasc and non-aesthetasc sensilla for orientation under the current experimental conditions. Other behavioral studies suggest that a lobster's capacity to perform odor learning and discrimination is also only marginally diminished following aesthetasc ablation (4). Future studies using more complex stimuli and flow environments may help to distinguish the functions of these two pathways.

Supported by NSF IBN 0077474 and NIH DC00312

References:

1. Cate H.S. and Derby C.D. 2000. A novel chemo-mechanosensillum that is widely distributed on the Caribbean spiny lobster and other lobsters. Chem. Senses 25: 633-634.

2. Schmidt M., Van Ekeris L., and Ache B.W. 1992. Antennular projections to the midbrain of the spiny lobster. I. Sensory innervation of the lateral and medial antennular neuropils. J. Comp. Neurol. 318: 277-290.

3. Schmidt M. and Ache B.W. 1992. Antennular projections to the midbrain of the spiny lobster. II. Sensory innervation of the olfactory lobe. J. Comp. Neurol. 318: 291-303.

4. Steullet P., Kruetzfeldt, D., Hamidani G., Flavus T., and Derby C.D. 2000. Functional overlap of two antennular chemosensory pathways in food odor discrimination behavior of spiny lobsters. Chem. Senses 25: 671.

 


14

M. Kakiuchi, M. Miyama, R.Yamaoka , M. Ozaki

Department of Applied Biology
Faculty of Textile Science
Kyoto Institute of Technology,Kyoto Japan
[email protected]

Experimental effects of flower odors on feeding preference in the blowfly

It is conceivable that flower-visiting insects recognize and memorize the flower odors associated with the food resources. Is their cognition of flower odors as the sign of food resources obtained a posteriori by experience, or regulated a priori? We used the blowflies, Phormia regina, examined the influences on food recognition caused by the experience of feeding sucrose flavored with various flower odors, the complex mixtures of volatiles.

The flies had been exposed to the flower odor while being fed with 0.1Msucrose for six days after their eclosion. Then we measured the feeding preference with quantitative feeding behavioral experiment. In this experiment, we found blowflies connately have positive or negative preference on the flower odors for their diet. Furthermore, we showed that the feeding preferences of the blowflies were alternated by flavored diet experience. These results imply that associative memories of flower odor with taste of diet influence feeding preference of the flies.

 


15

B. Kalinová1 and B. S. Hansson2

1 Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2

2 Department of Ecology, Lund University SE-223 62 Lund, Sweden
[email protected]

Characterisation of antennal olfactory receptor cells in the male moth Manduca sexta sensitive to non-pheromone odours

Moths posses highly specialized olfactory capabilities that enable them to locate e.g. food, mating partners, and places to oviposit. Much is known about the structure and function of the moth olfactory system with respect to male detection of conspecific sex pheromones. However, despite the fact that pheromone information is processed and analyzed only in a relatively small sub-compartment of the male olfactory system, we lack an understanding of broader olfactory capabilities of the male. We investigated the physiology of antennal olfactory receptor neurons (ORN)s in the male moth Manduca sexta sensitive to odorants that are not components of the pheromone blend. The physiological responses of ORNs to 27 floral and host-plant related volatiles show that M. sexta males detect non-pheromonal stimuli, similarly to pheromonal ones, by means of great number of sensitive ORNs with a narrow receptive range. Olfactory sensilla housing plant-odour and pheromone-detecting neurons were separated into different antennal regions. The only exception was found for Z11-hexenylaldehyde, one of the minor pheromone components. Sensilla housing Z11-specific ORNs were scattered among plant-odour detecting sensilla. When comparing male sensory abilities with those found in females, it became evident that both males and females hold ORNs with similar olfactory capacity to detect non-pheromonal odors. An electroantennographic study does however suggest that female antennae have a higher number of ORNs sensitive to non-pheromone stimuli than males.

 


16

Min Levine , William Walthall, Phang Tai, Paul Harrison and Charles Derby

Department of Biology
Georgia State University
Atlanta, Georgia USA
[email protected], [email protected]

A CUB-serine protease in the olfactory organ of the spiny lobsters Panulirus argus: cloning, in situ expression, and possible function

A gene encoding a protein product with high sequence identity to trypsin-like serine protease and CUB was identified from a cDNA library of the olfactory organ (i.e. antennular lateral flagellum) of the Caribbean spiny lobster Panulirus argus. The full-length cDNA sequence is 1802 bp, encoding a 50.251 kD protein with three domains. The 1st domain is a signal sequence, indicative of a secreted protein. The 2nd domain is a CUB, named after the Complement subcomponents Clr / Cls, Uegf, and Bone morphogenic protein (2). The 3rd domain is a trypsin-like serine protease. To detect the expression of this CUB-serine protease (CSP), antibodies were generated. RT-PCR and Northern and Western blot gels showed that this gene is predominantly expressed in antennular lateral flagella and in the eye, but not in brain, antennular medial flagella, abdominal muscle, hepatopancreas, intestine, and legs; there may be trace amount of the expression in the second antennae and the dactyl tips. As with the lobster CSP, in other species, CUB and serine protease domains are often encoded in the same protein (1,2,5,7,9). These proteins typically are secreted and often function in regulation of neural development (1,2,5,7,9). Serine proteases have also been suggested to function in chemoreception of marine invertebrates, where they may play a role in perireception through enzymatic generation of active chemostimulants from inactive precursors (3,10). Immunocytochemistry using an antibody generated to the lobster CSP shows that in the lateral flagellum (4), CSP is present in and around the auxiliary (glial) cells that envelope the inner dendritic segments of mature aesthetasc olfactory receptor neurons (ORNs) and around the entire length of the outer dendritic segments (i.e. in the lumen of the aesthetasc distal to the aesthetasc auxiliary cells). This suggests that CSP is expressed by aesthetasc auxiliary cells and secreted into the lumen of the aesthetascs. CSP is expressed in all molt stages and in auxiliary cells associated with ORNs at all developmental ages (6,11,12); however, the precise pattern of expression appears to differ somewhat with molt stage. In the eye, CSP also appears to be expressed in glial cells, but mostly in glia surrounding axonal tracts that connect neuropils in the eye. We propose that in olfactory organ of P. argus, CSP is expressed in glial cells surrounding ORNs, secreted out of the glial cells, associates via the CUB domain with the dendritic cell membrane of ORNs, and has trypsin-like activity in the extracellular environment. The CSP may function in perireception (by activating or inactivating odorant stimuli in the sensillar lymph), in maintaining and regulating dendritic growth and function of mature ORNs, or in molting of the olfactory system of the spiny lobster. It may also function in the maintenance of the function of mature sensory neurons in the eye. Our results, together with preliminary reports of different serine proteases and their inhibitors in the olfactory organ of lobsters (8,13), suggests that this class of molecules may be important in olfaction.

Supported by NIH DC00312 and NSF IBN 0077474.

References:

1. Baird J.L. and Rapier J.A. 1995. A serine protease involved in contact mediated repulsion of retinal growth cones by DRG neurites. J. Neurosci. 15: 6605-6618.

2. Bork, P and Beckmann G. 1993. The CUB domain. A widespread module in developmentally regulated proteins. J. Mol. Biol. 231: 539-545.

3. Brown K.A., Tamburri M, and Zimmer-Faust R.K. 1998. Modelling quantitative structure-activity relationships between animal behaviour and environmental signal molecules. J. Exp. Biol. 201: 245-258.

4. Grünert U. and Ache B.W. 1988. Ultrastructure of the aesthetasc (olfactory) sensilla of the spiny lobster Panulirus argus. Cell Tiss. Res. 251: 95-103.

5. Gschwend T.P, Krueger S.R., Kozlov S.V., Wolfer D.P., and Sonderegger P. 1997. Neurotrypsin, a novel multidomain serine protease expressed in the nervous system. Molec. Cell. Neurosci. 9: 207-219.

6. Harrison P.J.H, Cate H.S., Swanson E.S., and Derby C.D. 2001. Post-embryonic proliferation in the spiny lobster antennular epithelium: rate of genesis of olfactory receptor neurons is dependent on molt-stage. J. Neurobiol. 47: 51-66.

7. Hecht P.M. and Anderson K.V. 1992. Extracellular proteases and embryonic pattern formation. Trends in Cell Biology 2: 197-202.

8. Hollins B., Schweder D., and McClintock T. 2000. Identification of messenger RNAs enriched in the lobster olfactory organ. Chem. Senses 25: 646 (abstract).

9. Misra, S., Hecht P., Maeda R., and Anderson K.V. 1998. Positive and negative regulation of Easter, a member of the serine protease family that controls dorsal-ventral patterning in the Drosophila embryo. Development 125: 1261-1267.

10. Rittschof D. 1993. Body odors and neutral-basic peptide mimics: a review of responses by marine organisms. Amer. Zool. 33: 487-493.

11. Steullet P., Cate H.S., Michel W.C., and Derby C.D. 2000. Functional units of a compound nose: aesthetasc sensilla house similar populations of olfactory receptor neurons on the crustacean antennule. J. Comp. Neurol. 418: 270-280.

12. Steullet P., Cate H.S., and Derby C.D. 2000. A spatiotemporal wave of turnover and functional maturation of olfactory receptor neurons in the spiny lobster Panulirus argus. J. Neurosci. 20: 3282-3294.

13. Stoss T.D., Derby C.D., and McClintock T.S. 2001. Transcripts enriched in the proliferation zone of the lobster olfactory organ. Abstract from AChemS XXIII.

 


17

J.F. Picimbon, D. Abraham and C. Löfsted

Department of Ecology
Lund University, 223-62 Lund, Sweden
[email protected]

Variability of Pheromone-Binding Protein subtypes in moths

The sensory neurons are bathed by a lymph which constitutes a hydrophilic barrier for airborne pheromone stimuli. A class of specific proteins, the Pheromone-Binding Proteins (PBPs), may be involved in the transport of hydrophobic pheromone molecules en route to olfactory neurons. We have shown that noctuiid species that use multicomponent pheromones express two types of PBPs, PBPs of class 1 (PBP1) and PBPs of class 2 (PBP2). These two classes show about 50% identity. The comparison of PBP sequences obtained in two noctuiid species, Agrotis ipsilon (1,2) and Mamestra brassicae (3), reveals that PBP1s show 71% identity whereas PBP2s are more conserved (about 85% identity). This suggests that noctuiid species may express a conserved (PBP2) and a more variable (PBP1) type of PBP. We have analysed the variability of PBP1 and PBP2 in phylogenetically distant species of moths, belonging to the Noctuoidea and Geometroidea superfamilies, and discuss the functional importance of each PBP sub-type.

References:

1. Picimbon J.F. , Dietrich K. , Gadenne C. , Krieger J. , Prestwich G.D. and Breer H. 1999. Diversity and properties of odorant binding proteins (OBPs) and chemosensory proteins in moths. ISCE-Abstracts 0-3.

2. Picimbon J.F. , Gadenne C., and Prestwich G.D. 2001. Recognition of multicomponent pheromone: identification of pheromone-binding proteins in the black cutworm moth, Agrotis ipsilon. Insect Biochem. Molec. Biol. submitted.

3. Maibeche-Coisne, M. , Jacquin-Joly, E. , Fran_ois, M.C. and Nagnan-Le Meillour, P. 1998. Molecular cloning of two pheromone binding proteins in the cabbage armyworm Mamestra brassicae. Insect Biochem. Molec. Biol. 28:815-818.

 


18

C. McMahon & P.M. Guerin

Institute of Zoology
University of Neuchâtel, Rue Emile-Argand 11, Neuchâtel 2007, Switzerland
[email protected]

Attraction of ticks to vertebrate breath and its components.

Vertebrate breath is a complex host emanation consisting of several active compounds that together constitute a potent host marker for many haematophagous arthropods. Our study concerned the directed and locomotory responses of ticks, particularly of Amblyomma variegatum adults, to breath components and their mixtures while walking in an air stream on the Kramer locomotion compensator (servosphere). Although diluted breath with 0.15% CO2 proved attractive, its principal component CO2 was only attractive on its own at low concentrations ( ¾ 0.015%) and became significantly less attractive as dose increased. The attraction to both diluted breath and CO2 differed from other attractive breath compounds such as acetone in that they elicited a smooth rather than tortuous walk towards the odour source. It thus appears that the presence of CO2 modifies, and is modified by, other chemicals in the breath mixture. This reinforces the concept that attraction to a single component at a high concentration (in our case CO2 in breath) can be maintained in the presence of an optimal blend.

 


19

Mamiko Ozaki, Mayako Kakiuchi, Teruhiko Takahara and Ryohei Yamaoka

Department of Applied Biology
Faculty of Textile Science
Kyoto Institute of Technology, Kyoto, Japan
[email protected]

Taste reception of lipophilic oral toxins via an odorant-binding protein in the blowfly.

Investigation on tastes of oral toxic substances is difficult to be conducted, because the test animal, which may take such toxic chemicals during the experiments, would not keep stable condition. Fortunately, insect chemosensilla can be stimulated with a toxic substance without killing the animal.

1. Oral toxicity of the chemicals: Using D-limonene and some other mono-terpenes, we first examined their oral toxcity for the blowfly, Phormia regina, and found the following order of toxcity; D-limonene>L-limonene>mycene>citral>toluene When the taste sensilla of the blowfly was touched with D-limonene, the fly exhibited aversive behavior accompanied by tipping and excretion.

2. Taste response of the chemicals: These chemicals are lipophilic but could be dissolved in a aquatic solution with an odorant-binding protein found comonly in the olfactory and taste sensilla of the blowfly. We could then obtain taste response to them from the fifth cell (the fourth taste receptor cell). This suggested that the fifth cell send a sign of toxin to the brain, which induced aversive behavior of the fly.

3. Appetite reduction induced by smells of the chemicals: Vapors of these chemicals did not affect duration of life time of the fly. However, their smells or even the memory of the smells obviously decreased the sensitivity of prpboscis extension reflex and the amount of food which they actually ate. We also measured mono-amines in the brain and found some differences between the flies thus reduced in their appetite and the control flies showing normal appetite.

In order to save their lives, the flies, when exposed such dangerous smells, may reduce appetite. Even if they touch the toxic chamicals, the fifth cell responding to them would prevent the flies from eating.

 


20

D. Picone1, O. Crescenzi 2, A. Scaloni 3, S. Angeli4 and P. Pelosi5

1 Dipartimento di Chimica, University Federico II, 80100 Napoli, Italy
2 Dipartimento di Chimica Organica e Biochimica, University Federico II, 80100 Napoli, Italy
3 I.A.B.B.A.M. - Centro Internazionale Servizi di Spettrometria di Massa, CNR, via Argine 1085, 80147 Napoli, Italy
4 Scuola Superiore SSSUP "S. Anna", 56124 Pisa, Italy
5 Dip. Chimica e Biotecnologie Agrarie, via S. Michele, 4, 56124 Pisa, Italy
[email protected]

Structure and function of Chemosensory Proteins (CSP) in insects

Chemosensory proteins (CSPs) is the name given to a class of small soluble proteins found in chemosensory organs of insects. Some charcteristics suggest that they represent a second class of binding proteins for chemical stimuli. These proteins are slighly smaller than OBPs, generally, but not always acidic and very soluble. Like OBPs, their concentration in chemosensory structures is extremely high. The first protein of this class was identified in Drosophila, later members were described in most insect Orders, from the very primitive Phasmids to Lepidoptera and Hymenoptera. Their amino acid sequences are better conserved than OBPs, with an average of about 40% of common residues, even between very distant species. In apparent constrast with this charactersistics, polyclonal antibodies raised agaist CSPs of different species do not cross-react. Two pairs of nearly adjacent conserved cysteines are linked by two disulphide bridges, that apparently do not contribute to the three-dimensional structure of the molecules. Immunocytochemical experiments have indicated that they are highly concentrated in the sensillar limph of chemosensory hairs. Members of this family have been identified in the ejaculatory bulb of Drosophila, the same organ secreting the sex pheromone, and in subcuticular cells. The protein extracted from this latter source contains, as endogenous ligands, long-chain hydrocarbons. These observations seem to indicate that CSPs might be involved, not only in the perception, but also in the release of pheromones. We have expressed one of the CSPs of Schistocerca gregaria and the Drosophila OS-D in bacterial systems, in order to produce antibodies for immunocytochemical localisation and to obtain enough protein for structural studies. The CSP of S. gregaria has also been obtained in N-15 enriched form and used in NMR conformational studies. We report preliminary data on the three-dimensional structure of this protein, composed of six alpha-helices

 


21

L. P. Ban 1, A. Brandazza2, S. Angeli3, L. Zhang3, Y.H. Yan1 and P. Pelosi 2

1 Department of Entomology, China Agricultural University, Beijing 100094, China
2 Dip. Chimica e Biotecnologie Agrarie, via S. Michele, 4, 56124 Pisa, Italy
[email protected]
3 Scuola Superiore SSSUP "S. Anna", 56124 Pisa, Italy

Purification of Chemosensory Proteins (CSP) in Locusta migratoria

Locusta migratoria represents the major pest in Asia, producing enourmous damage to crops. Based on our previous information on the related species Schistocerca gregaria, we have started investigating the biochemical mechanisms of chemical communication in this insect, focusing our attention on soluble proteins of chemosensory organs.

Electrophoretic analysis both in native and denaturing conditions of crude extracts of antennae, tarsi and palpi, revealed the presence of acidic proteins of low molecular weight. Some of these bands were present only in antennal extracts, while others were present also in tarsi and palpi. These proteins were purified by gel filtration chromatography, followed by preparative electrophoresis in native conditions.

N-terminal sequences have indicated such proteins to be members of the family of Chemosensory Proteins (CSPs). Amplification of the relative genes by PCR with degenerate primers, cloning and sequencing allowed the establishment of nucleotide sequences encoding several members of this group. Their derived amino acid sequences share about 90% of their residues with CSPs of S. gregaria and between 50 and 60% with those described in L. migratoria.

Polyclonal antibodies have been raised in mice agains the protein purified from the antennae and are currently used in immunocytochemistry experiments to label its sites of production and accumulation within the chemosensory organs.

Western blot experiments have been used to monitor the expression of these proteins during the developmental stages of the insect.

As in the case of S. gregaria, a similar protein was purified from the wings, where it is associated with organic compounds of low volatility, whose structures are currently being investigated.

 


22

Jean-François Picimbon 1*, C. Gadenne**, C. Löfstedt*

1 Alexander von Humboldt, c/o Prof. H. Breer, Institute of Physiology
University of Hohenheim, Garbenstrasse 30, 70593 Stuttgart, Germany
*Department of Ecology, Lund University, Sölvegatan 37, SE-22362 Lund, Sweden
** INRA, Unité de Recherches en Santé Végétale, 33883 Villenave d'Ornon, France
[email protected] ,[email protected]

Interpopulational variations and ultradiversity of "Antennal Binding Proteins X" (ABPX) in the black cutworm moth, Agrotis ipsilon (Lepidoptera, Noctuidae)

The olfactory cues orientate the moth larvae to feed preferentially on the diet on which they have been reared. Therefore, the odorant environment may induce specific variations in the olfactory system of insects. A world-widespread migrant species like the black cutworm moth, Agrotis ipsilon, which habitates different continents is likely exposed to different external (odorant) environments and may therefore constitute an appropriate model to test this hypothesis and to study in particular the interpopulational variations of the expression of antennal odorant-binding proteins (OBPs). The OBPs are proteins extremely concentrated in the "lymph" in which the sensory neurons of a sensillum are bathed; they represent effective shuttle proteins that ferry the odorant molecules across the lymph from the cuticular pores to the sensory receptor neurons. In insects, a particular class of OBPs may mediate the transport of generalist odorants like plant volatiles: the general odorant-binding proteins (GOBPs). Another class of OBP including the antennal binding proteins X (ABPXs) and counterparts from phylogenetically distant insects may have a similar function.

The GOBP2 of A. ipsilon (AipsGOBP2) shows no interpopulational differences. However, we have shown that two intercontinental (European and American) populations of A. ipsilon display specific variations in the expression pattern of ABPX (AipsABPX). AipsABPX-1-encoding messenger RNAs are detected in both American and European populations but differences are found in mRNA and protein levels, AipsABPX-1 being preferentially expressed in the European population.

This suggests the existence of post-transcriptional control mechanisms of the expression of OBP genes. The American population may better express another type of ABPX. In A. ipsilon, we have revealed an ultradiversity for ABPX. Noctuiid species seem to express a conserved (class 1) and a more variable (class 2) type of ABPX. ABPXs of class 1 show about 80% identity between each other; they show 58-62% to ABPXs of other species of moths but only 28-35% identity to ABPX-related proteins of scarab beetles, true bugs and Drosophila melanogaster (PBPRPs). ABPXs of class 2 display only 58% identity between each other and 24-32% identity to PBPRP-5 and PBPRP-2. ABPXs related to PBPRP-4 may represent a third class of ABPX. In addition, we have observed that subtle switches in the nucleotide sequence of ABPX-1 lead to specific amino acid replacements and thereby to a microdiversity of ABPX. Altogether, these results strongly support the existence of a potentially enormous variety for ABPX. The raisons d'être of ultradiversity and interpopulational variability of ABPX are unknown. However, it is likely that such a large repertoire of OBP in combination with specific environment-dependent post-transcriptional controls of the OBP expression would certainly allow Insects to perfectly "fit" with their odorant environment.

 


23

Dainius Plepys1, Fernando Ibarra2, Bill S. Hansson1, Wittko Francke2 and Christer Löfstedt1

1 Department of Ecology, Lund University, SE-223 62 Lund, Sweden
2 Institute of Organic Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany
[email protected]

Odour-mediated nectar foraging in silver Y moth, Autographa gamma

It is well established that floral odours play a significant role in the nectar foraging behaviour in Lepidoptera and other insect orders. Floral odour may elicit searching, alighting and feeding behaviours alone or in concert with visual stimuli. At present there are more than 700 scent compounds from more than 400 species of plants identified. The large number of compounds produced by a flower hampers the elucidation of their behavioural activity. Behaviourally active compounds often show striking electrophysiological activity. Thus, electrophysiological data may provide useful information, limiting the number of compounds to be tested in behavioural experiments. However, at present little is known about as to which floral compounds can be perceived by insects¹ nervous system and even less about their behavioural role.

In a flight tunnel assay we investigated the attractivity of selected flowers to the silver Y moth A. gamma (Lepidoptera: Noctuidae) and identified the constitutents of floral scents responsible for this attraction. We tested the following plants with flowers that are visited by A. gamma or other noctuid moths: catnip Nepeta faasseni (Labiatae), butterfly-orchid Platanthera bifolia (Orchidaceae), red clover Trifolium pratense (Fabaceae), creeping thistle Cirsium arvense (Asteraceae), greater knapweed Centaurea scabiosa (Asteraceae) and soapwort Saponaria officinalis (Caryophyllaceae). Volatiles from all plant species were collected, analysed for electrophysiological activity by gas chromatography with electroantennographic detection (GC-EAD) and the active compounds were indentified by coupled gas chromatography/mass spectrometry (GC-MS). We also identified behaviourally active constituents of P. bifolia floral odour. Lilac aldehydes were found to be the major behaviourally active compounds. We discuss reasons for differential attraction to flowers, plant-species specific volatiles and overlap in profiles that have been observed between plant species.

 


24

Blanka Pophof

Max-Planck-Institut für Verhaltensphysiologie, Seewiesen
[email protected]

Inhibition of the transduction process in silkmoth olfactory receptor neurons

Electrophysiological responses of olfactory receptor neurons (ORNs) in both male and female silkmoths Bombyx mori were investigated. In both sexes, the G-protein activator sodium fluoride (NaF) and the diacylglycerol analog dioctanoylglycerol (DOG) elicited nerve impulse responses similar to those elicited by weak continuous stimulation with odorants. Therefore, G-proteins and diacylglycerol activated ion channels seem to be involved in the transduction process in both pheromone sensitive ORNs (found in males) and general odorant sensitive ORNs (found in females).

Decyl-thio-trifluoro-propanone (DTFP) is known to inhibit electrophysiological responses of moth pheromone sensitive ORNs, but has no effect in females (1). General odorants, like e.g. linalool, excite ORNs in females, but inhibit the pheromone sensitive ORNs in males (2, 3). At the level of elementary receptor potentials (bumps) which can be elicited by single pheromone molecules and seem to reflect ion channel openings, DTFP reduces the frequency of bumps. In contrast, application of linalool reduces the amplitude of bumps but not their frequency. Both effects reduce the amplitude of the overall receptor potential in response to pheromone. Application of DTFP has no inhibitory effect on electrophysiological responses elicited by NaF or DOG. This supports the idea presented earlier (1) that DTFP acts on a prior step of the transduction cascade, e.g. on the pheromone receptor molecules. On the other hand, both linalool and heptanol inhibit the responses of pheromone sensitive ORNs elicited by NaF or DOG. Therefore, these compounds seem to inhibit later processes of the transduction cascade in pheromone receptor cells, possibly directly the ion channel opening. An inhibitory effect of linalool has also been shown for the CNG-gated channels of ORNs in vertebrates (4).

References:

1. Pophof B. et al. (2000) J. Comp. Physiol. A 186: 315-323

2. Kaissling K.-E. et al. (1986) J. Comp. Physiol. A 165, 147-154

3. Heinbockel T. & Kaissling K.-E. (1996) Insect Physiol. 42: 565-578

4. Kawai F. & Miyachi E. (2000) Brain Research 876: 180-18

 


25

Stéphane Rivière and Rémy Brossut

CNRS UMR 5548 - Université de Bourgogne
6, Bd Gabriel, 21000 Dijon, France
[email protected]

Molecular identification of two new OBP in an Heterometabolous Insect: Leucophaea maderae (Dictyoptera, Oxyhaloinae)

Chemosensory information is required for foraging and mating in cockroaches. These behaviors rely on the ability to detect and discriminate olfactory signals. These stimuli are mediated by insect olfactory receptors (ORs) located in the sensillar hairs widely found on the olfactory organs (antenna and maxillary palps). Within the sensillar lymph, olfactory binding proteins (OBPs) carry the odorants toward the ORs. Although OBPs have been described in several Holometabolous insect orders, only one OBP has been described so far in a heterometabolous insect (Lygus lineolaris, Heteroptera).

The goal of our study was to find cDNAs corresponding to such proteins in the cockroach L. Maderae. A RT-PCR approach with degenerate primers was performed and two fragments were cloned. The deduced protein sequences were homologous to the OBP family. Northern blot analysis and in situ hybridization studies detected the transcript of the first fragment in the maxillary palps of both sexes whereas the transcript of the second fragment specifically in the female antennae. As the sexual pheromone blend is emitted by males and detected by females, in this species, we suspect that this latter OBP may be a pheromone binding protein (PBP). Moreover PBP-Lma showed significant sequence similarity with lepidopteran and dipteran PBPs proteins.

Our results provide the first identification of OBP and PBP in Dictyoptera. Furthermore the expression pattern of these two OBPs seems very close to the pattern described in numerous species. This supports the general hypothesis that OBPs play a role in odor perception in both holometabolous and heteometabolous insects.

 


26

Maria D. Setzu1, Felice Loffredo2, Marco Piludu2, Ignazio Collu1 and Anna Maria Angioy1

1 Department of Experimental Biology ­ Section of General Physiology
University of Cagliari, I 09042 Monserrato-Cagliari, Italy
2 Department of Cytomorphology-Electronic Microscopy Laboratories
University of Cagliari, I 09042 Monserrato-Cagliari, Italy
[email protected], [email protected]

Fine structure and distribution of olfactory sensilla on the antennal flagellum of the blowfly Protophormia terraenovae

Olfaction plays a fundamental role in guiding orientation behaviours of insects, including oviposition, feeding and mating. In blowflies, the antennae are the primary olfactory organs bearing olfactory receptors through which they perceive a variety of odours. Although some aspects of their functional morphology and physiology have been described, no detailed examination of the blowfly olfactory system has been reported.

In the present study, the fine structure and distribution of sensilla types on the basal subsegment of the antennal flagellum of Protophormia terraenovae blowflies were investigated by scanning and transmission electron microscopy, as an essential base for physiological investigations which are in progress in our laboratory.

At rest, antennae fit in a concavity of the head capsule, thus resulting frontally exposed to air against wind. Only when antennae are extended forward are they fully exposed to air with the dorsolateral, dorsomedial and ventral surfaces. The two dorsal surfaces are thickly clothed with many uniformly distributed types of hair-like structures. Such structures are also present on the ventral surface, but with a distribution that can hardly be considered uniform, especially in its proximal-medial region. This region is roughly bordered on its lateral and medial sides by a number of pits, some of which are simple pocket-like cavities while other are quite complex multichambered assemblies. No sex-related differences, either in flagellum size or in the total area of pit openings in the ventral surface of the flagellum, have been found.

Among hair-like structures, a dense population of non-innervated hairs of various sizes and nine morphological types of sensilla have been identified: one coeloconicum and two grooved peg types are located within the pit area, while one basiconic, one auriculate, two trichoid types of sensilla and two grooved peg types are located on the flagellum surface externally to pits.

The three types of pit sensilla present porous walls and contain two sensory neurons. A first type of the two grooved pegs is double-walled and is located in ventrolateral pits, while a second type of grooved peg and the coeloconicum sensillum are single-walled and are situated in ventromedial pits.

Among sensilla distributed externally to pits on flagellum surfaces, the type A trichoid sensillum is the longest and most abundant one. The central lumen of this single-walled wall-pore sensillum contains the outer dendritic segments of three sensory neurons. The type B trichoid sensillum, a single-walled wall-pore sensillum containing three sensory neurons, is smaller and has a thinner wall compared to the type A trichoid one. In the type B sensillum, dendrites of two sensory cells branch extensively within the shaft, circularly wrapping up the larger dendrite of the third sensory cell in a regular way. The latter shows lamellar folding within the apical section. The basiconic sensillum is similar in size and wall features to the type B trichoid sensillum, from which it can be distinguished by a blunt tip and greater distribution density on flagellum surfaces. Two to three sensory cells are present in the sensillum, whose dendrites branch extensively distally. The spoon-like or ear-like auriculate sensillum, this too a single-walled wall-pore sensillum, is present in fairly good density only in an ample central area of the ventral surface of the flagellum. Grooved peg sensilla located externally to pits are distributed on both the dorsal and ventral surfaces of the flagellum. Their walls are longitudinally grooved in their distal half and present up to fifteen cuticular fingers which converge distally towards the sensillum tip. In a grooved peg type, the less abundant one, cuticular fingers are distally arranged around an apical opening. In a second and more numerous type of grooved peg, fingers end distally to a closed tip. Further ultrastructural details of these sensilla are still under examination. Functional considerations on the latter are thus postponed, while results obtained thus far indicate that the different types of sensilla described above present structural characteristics that are typical of insect olfactory sensilla.

Supported by: Italian Ministry of Universities and Scientific Research; Cape Carbonara Protected Sea Area.

 


27

H. Th. Skiri1, C. G. Galizia2 and H. Mustaparta1

1 Norwegian University of Science and Technology, Department of Zoology, Neurobiology
MTFS, N-7489 Trondheim, Norway
[email protected]
2 Institut für Biologi - Neurobiologie, Freie Universität Berlin
Königin Luise Str. 28-30, D-14195 Berlin, Germany

Spatial distribution of calcium responses to plant odour stimulation, measured in the antennal lobe of the moth Helitohis virescens

Previous electrophysiological and optical imaging experiments on Heliothis virescens males have shown that the macroglomerular complex (MGC) receives information about insect produced signals, whereas the ordinary glomeruli are activated by stimulation with plant odours. The MGC is not present in the female antennal lobe, and so far no responses to insect produced signals have been recorded in the females. There is a spatial representation of pheromone and interspecific signal information in the MGC, which seems to be conserved between individuals. Little is known about specific activation patterns of the ordinary glomeruli during stimulation with plant odours. In the present study, the calcium-sensitive dye Calcium-Green AM, was used to measure responses in the antennal lobe to stimulation with 11 single compounds and two mixtures at 5 different concentrations. Activity in the antennal lobe was obtained both as response to odours and sometimes as response to the control (air). The stimulation with plant odours elicited a distributed activity pattern in the ordinary glomeruli of both sexes, and individual glomeruli took part in the activity patterns of different odours. Individual glomeruli were identified using a 3D-atlas of the moth antennal lobe. The representation of the different plant odours appeared to be conserved between individuals of the same sex. Plant odour information in this moth species, like in the honeybees, is represented as an across-glomeruli code in the ordinary glomeruli.

 


28

Elisabetta Chiappini1, Chiara Solinas1, Mario Solinas2

1 Ist. Entomologia e Patologia vegetale, Univ. Cattolica Sacro Cuore, Piacenza (Italy)
2 Dip. Arboricoltura e Protezione Piante, Università di Perugia (Italy)
[email protected]

Antennal chemosensilla of Anagrus atomus (L.) (Hymenoptera: Mymaridae) female and their possible behavioural significance

The antennae of a female hymenopteran Mymaridae, Anagrus atomus (L.), have been investigated, through light microscopy as well as, for the first time, through scanning and transmission electron microscopy, principally aiming at identification of sensory structures possibly involved in reproductive behaviour. Topographic distribution of the external components (cuticular appendages) of sensilla have been illustrated through camera lucida semischematic diagrams of the whole antenna, and especially the club, together with scanning electron micrographs. Topographic location of the same sensilla internal (cellular) components have been shown in the antennal club through transmission electron micrographs from serial cross sections. Three categories of chemosensory structures have been identified (i.e., "apical sensilla", "sensilla trichodea Type 1", "sensilla trichodea Type 2", "sensory ridges") and illustrated through semischematic diagrams and transmission electron micrographs from fine serial sections. On the basis of the nature of the sensilla and their location on the antennae, together with antennal use during the female reproductive behaviour, the behavioural meaning of the above mentioned sensilla has been hypothesized.

The two "apical sensilla", set on the club tip, consist of a basiconic, relatively long , uniporous hair, and cellular components represented by three sensory neurons and only one, big sheath cell. All the sensory neurons send their outer dendritic segments into the hair-shaft lumen, reaching almost to the tip. They might be gustatory, although the hair-shaft lumen lacks a distinct dendritic channel, the outer dendritic segments are naked all their length, and there is no mechanosensitive element. They are most probably involved in the recognition of the microhabitat, i.e., the host-plant tissue wounded by the leaf-hopper ovipositor. In fact, the Anagrus female walks quickly up and down on the wounded leaf, in search of the host eggs, bearing the antennae slightly diverging, directed towards the leaf surface so as to form a 50° angle with the latter, and constantly tapping the substratum with her antennal club tips; furthermore the tapping frequency increases while the female slows her walking on finding a leaf-hopper egg.

The 6 "sensilla trichodea Type 1", mostly distributed subapically on the club ventral side, are also uniporous, and possess cellular components consisting of four sensory neurons and only one sheath cell. Of the four sensory neurons, three send the outer dendritic segments into the hair-shaft lumen while the fourth one terminates with a tubular body at the hair-shaft base, thus representing a mechanosensitive element. Morphologically speaking, these sensilla must be considered gustative although the hair-shaft lumen lacks a distinct dendritic channel, and the dendritic sheath is unusually developed. They are most probably involved in examination/selection of the host eggs. In fact, after the piece of behaviour reported above, the Anagrus female, bearing its antennae almost parallel to each other, repeatedly brushes the scar above the host egg with the antennal club ventral side.

The 9-10 "sensilla trichodea Type 2", distributed on the club ventral side, are externally very similar to the Type 1sensilla but the cellular components consist of five sensory neurons and two sheath cells. Of the five neurons, four have outer dendritic segments which enter the hair-shaft lumen, unbranched and still encased in the dendritic sheath; while the fifth neuron ends with a tubular body at the hair-shaft base, thus representing a mechanosensitive element. Morphologically speaking, these sensilla must be contact-chemoreceptors, just like Type 1. Their behavioural significance must be similar to that of the latter, but probably tuned to different substances, i.e., the host plant sinomones and the host egg kairomones, alternatively. The problem might be resolved through electrophysiological bioassays.

The 3 "sensory ridges" (Auctorum), are conspicuous thick-walled sensilla with bell-shaped pores, longitudinally located one on the medial and two on the lateral side of the club. The cellular components of each sensillum consist of some twenty sensory neurons and two sheath cells. Morphologically speaking, these sensilla must be olfactory, and they are apparently involved in the microhabitat (i.e., a leaf of the leaf-hopper host-plant potentially bearing eggs) recognition. In fact, an Anagrus female introduced into a Petri dish and presented with a host-plant leaf bearing leaf-hopper eggs, just before leaping onto the leaf, stops walking and keeps the antennae in an upright position, slightly rotating them, as it were to capture airborne odour molecules and to establish their provenience.

Supported by the Italian MURST ex 40%, Project "Chemoreceptors and Semiochemicals involved in Interactions between Insects and relative host-plants", Co-ordinator Prof. Mario Solinas.

 


29

X. Grosmaitre, M. Renou, F. Marion-Poll

Octopamine effect on olfactory receptors : sensitivity enhancement or adaptation inhibition ?

Mamestra brassicae male antennae bear pheromone-sensitive sensilla that house two neurones with different sensitivities. Neurone A responds to the major component of the female pheromonal blend (Z11-16:Ac or compound A) while neurone B responds principally to an interspecific inhibitor (Z11-16:OH : compound B). We have shown that octopamine (OA) enhanced the sensitivity of neurone A towards low doses of compound A, while the sensitivity of neurone B to low doses of compounds B remained the same. However, responses of neurone A and of neurone B to high doses of their best stimulus were higher after OA injection.

These results are unexpected unless one postulate that OA is either expressed differently or drive different transduction pathways in neurone A and neurone B. This might not be true. We rather postulate that the two neurones respond in the same way to OA, but that these differences originate from our experimental procedure. Compound A was used routinely as a standard stimulus across which responses to other chemicals were compared, while compounds B were used less frequently. This could result in different levels of long-term adaptation in the two neurones. Thus most parsimonious hypothesis is to postulate that OA modulate the adaptation state of the neurones.

This hypothesis is consistent with the aforementioned results. Assuming that neurones A were adapted before presentation of the stimulus, one would expect the response to be increased at all concentrations, even the lowest one. Likewise, assuming that neurones B were not adapted, one should expect an effect to be seen only after presentation of the highest doses of stimulus. Consistent with this hypothesis is also the observation that neurones A increased their firing activity in the absence of odorant stimulation, following an OA injection. This OA-dependent excitation is reduced after capping the sensilla with the recording electrode, thus preventing most odorant molecules to access the dendrites. Furthermore, we did not observe any OA-dependent excitation in a laboratory where compound A was never used before.

 


30

Zainulabeuddin Syed1, Susantha Mohottalage2, Patrick Guerini1, Raphael Tabacchi2

1 Institute of Zoology, Emile-Argand 11
University of Neuchatel, CH-2007, Switzerland
2 Institute of Chemistry, Av. Bellevaux 51
University of Neuchatel, CH-2000, Switzerland
[email protected]

Evidence for a role of habitat related compounds on tsetse behaviour

It has been argued that tsetse flies evolved from the forest and riverine habitats to colonise relatively dry savannah characterised by dry grasslands and dispersed trees. The current classification of tsetse is broadly based on habitat, placing them in three sub-genera i.e., the forest (fusca), riverine (palpalis) and savannah (morsitans) groups. Tsetse flies spend most of their lives resting on plants and spend only a short time (~30 min/day) in search of a host for a blood meal. Whereas modalities governing host searching behaviour have been thoroughly studied and exploited in devising tsetse fly traps, relatively little attention has been given to responses to stimuli from the habitat. Our research provides evidence that tsetse flies selectively respond to habitat related products in addition to host odours. Electrophysiological and behavioural experiments to be presented indicate that these compounds are perceived by species from all three tsetse fly groups.

 


31

Jonathan D. Bohbot, Richard G. Vogt

Dept. of Biological Sciences
University of South Carolina
715 Sumter St., Columbia , SC 29205, USA
[email protected]

Use of Quantitative Real-Time PCR to Investigate mRNA Expression Levels in Insect Antenna

The study of gene expression can be difficult in insects due to the relatively small tissue size yielding only minute amounts of mRNA and the difficulty in quantifying such small amounts of specific mRNAs. Quantitative PCR has been an option, amplifying small amounts of specific cDNAs; in this technique the quantity of a cDNA was estimated based on the number of reactions required to produce a certain quantity of final product. More recently, instrumentation has been developed which monitors the rates of product accumulation during the course of the reaction (Real Time), allowing for a more accurate and rapidly achieved quantitative estimate of cDNA levels. QRT-PCR is based on detection of a fluorescent signal produced proportionally during amplification of a PCR product.

We have two biological models where we are using QRT-PCR to analyze both static and dynamically changing levels of mRNA. The first model looks at the tissue specificity of an Odorant-Binding Protein Related Protein (OBPRP). This gene was cloned from an antennal cDNA library from the mosquito Aedes aegypti; we are using QRT-PCR to investigate the tissue specific expression of this gene while minimizing the number of individual animals required per assay. The second model looks at the temporal expression of three developmental markers involved in the establishment of the olfactory neuroepithelium of Manduca sexta during metamorphosis. These markers are Distal-less (DLL), Notch and Pupal-Cuticle Protein (PCP). DLL is a homeodomain transcription factor. Among its numerous functions, DLL patterns the developing antenna during pupation. Notch is a cell surface receptor that plays an important role during neurogenesis (1) and PCP is a structural protein involved in the establishment of the pupal cuticle. All three genes are dynamically expressed in a hormone dependent manner during the neurogenic period of adult antennal development. We hope to use the QRT-PCR assay to characterize the regulation of these genes during early development.

References:

1) Artavanis-Tsakonas, S. , Rand, M. D. & Lake, R. J.
Notch signaling: cell fate control and signal integration in development.
Science. 1999 Apr 30;284(5415):770-6. Review.
2) Kramer B, Wolbert P.
Down-regulation of expression of a pupal cuticle protein gene by transcriptional and posttranscriptional control mechanisms during metamorphosis in Galleria.
Dev Genes Evol. 1998 Jun;208(4):205-12

 


32

Christophe Gadenne1, Marie-Cécile Dufour1 and Sylvia Anton2

1 INRA, UMR Santé Végétale, Centre de Recherches de Bordeaux
BP 81, 33883 Villenave d¹Ornon cedex, France
2 Department of Ecology, Lund University
S-223 62 Lund, Sweden
[email protected]

Transient post-mating inhibition of behavioural and central nervous responses to sex pheromone in an insect

Mating is energy consuming in most organisms and should therefore only occur if it is likely to be successful. In moths, males produce a spermatophore, originating from the sex accessory glands, which is transferred into the female during mating. They need one more day to refill their glands in order to be able to produce a new spermatophore. Re-mating within the same night would thus be unsuccessful. We tested the hypothesis that newly mated males of the noctuid moth, Agrotis ipsilon, have developed a strategy to avoid unsuccessful matings based on the transient inhibition of their sexual behaviour. Our results show that newly mated A. ipsilon males do not re-mate during the same scotophase, and do not respond to the female sex pheromone although electroantennograms showed that their peripheral olfactory system is functional. Using intracellular recordings techniques, we showed that the sensitivity of antennal lobe (AL) neurons for the sex pheromone decreased significantly in newly mated males as compared with unmated males: the proportion of low threshold AL interneurons in newly mated males was significantly lower than in unmated males. Both the sexual behaviour and the sensitivity of the AL neurons were restored when tested during the next scotophase. Our results show a fast, transient neuronal plasticity, "switching off" the olfactory system, which could prevent males from mating unsuccessfully.

Supported by Swedish (SJFR) and French (INRA) Research Councils.

 


33

Thomas Kröber, Stoyan Grenacher, Patrick M. Guerin

Michèle Vlimant Institute of Zoology
University of Neuchâtel, Rue Emile-Argand 11, 2007 Neuchâtel, Switzerland
[email protected]

Behavioural and chemoreceptor cell responses of the sheep tick, Ixodes ricinus, to its own faeces and faecal constituents

Ticks are ectoparasites of vertebrates and utilise of infochemicals for intraspecific aggregation and mating responses. Individual male and female Ixodes ricinus, the vector of Lyme disease in Europe, readily arrest on filter paper strips contaminated with their own faeces. The faecal constituents guanine, xanthine, uric acid and 8-azaguanine (a bacterial breakdown product of guanine) caused arrestment of individual I. ricinus males and females. Mixtures of these products induced arrestment of I. ricinus at doses one hundred fold lower than the lowest active dose of any of them tested singly.

Saline extracts of faeces activated receptor cells in terminal pore sensilla on the first leg tarsi of I. ricinus. One cell in these sensilla responded in a similar dose dependent manner to guanine and 8-azaguanine, whereas a second cell was more sensitive to lower doses of 8-azaguanine. The response threshold approached 100 fM for both cells. These findings suggest that faeces and faecal breakdown products are implicated in aggregation responses of I. ricinus. This may account for the clumped distribution of this ectoparasite on the ground and contribute to the high proportion of mated individuals recorded prior to host colonisation.

References:

1. Grenacher, S., Kröber, Guerin, P.M., Vlimant, M. (2001) Behavioural and chemoreceptor cell responses of the sheep tick, Ixodes ricinus, to its own faeces and faecal constituents. Experimental & Applied Acarology 25, in press.

 


34

Philippe Jeanbourquin & Ted C. J. Turlings

Institut de Zoologie, Université de Neuchâtel
Case Postale 2, CH-2007 Neuchâtel, Switzerland
[email protected]

The relative attractiveness of Bt maize plants to two parasitoids of lepidopteran pests

The current discussion on the safety of transgenic crops includes their effects on beneficial insects. One aspect of particular interest is the herbivore-induced volatile emission by plants that attract natural enemies of herbivores. We have developed a six-arm olfactometer that permits the simultaneous collection of volatiles from various odour sources to compare the attractiveness of plants to various insects. With this system we compared the induced odour emissions of Bt maize (Bt11, N4640Bt) and its isogenic line (N4640) and the attractiveness of these odours to the two larval endoparasitoids Cotesia marginiventris and Microplitis rufiventris. The parasitoids are known to readily distinguish among odours of different intensity or quality and particularly C. marginiventris prefers odours that it has experienced during an oviposition. In this study both parasitoid species were attracted to olfactometer arms with maize odour and neither distinguished between the odours of the transgenic and isogenic line. Choices were divided equally among the two odours, also by wasps that had previously experienced one of the odours during a successful oviposition. Chemical analyses of collected odours revealed the presence of the same 11 dominant compounds in both genotypes. Some of these compounds were released in larger amounts by the isogenic plants. Apparently these differences were not detected by the wasps. All compounds have been previously identified from maize and the quantities in which they were released fall within the range of variability observed for other maize cultivars.

 


35

A. Liscia, C. Masala, G. Senes, P. Solari and R. Crnjar

Dipartimento di Biologia Sperimentale
Sezione di Fisiologia Generale
Università di Cagliari, Cittadella Universitaria di Monserrato
SS. 554 Km 4.500, I-09042 Monserrato (CA) ITALY
[email protected]

Sugar reception in the blowfly: a possible transduction mechanism

The present study addresses the problem of investigating the mechanisms underlying sweet taste transduction in the labellar chemosensilla of the blowfly Protophormia terraenovae by taking into account both the initial events after stimulation onset and those related to the adaptation process. The first goal was to verify whether a Ca++ current and/or Ca++ cascade is involved in sugar reception of the blowfly. To this end we tested the effect on the response of the "sugar" cell to both sucrose and fructose of: a) W-7 (a calmodulin antagonist, supposedly involved in the Ca++ cascade; Hidaka et al., 1981; Green and Gillette, 1988) and/or GDPbS (an inhibitor of G-protein); b) the addition of EGTA and BAPTA (well-known Ca++ chelating agents) to sugar solutions. Since in the receptor lymph of the taste hair Gödde and Krefting (1989) found a concentration of about 3mM/l Ca++, this study aimed at providing information on Ca++ current contribution to receptor potential.

The spike activity from the chemosensory cells in adult blowflies, Protophormia terraenovae, was recorded by means of the tip-recording technique (Hodgson et al., 1955). Our electrophysiological data indicate that W-7 addition strongly depressed the "sugar" chemoreceptor response to both sugars and in the case of sucrose stimulation also influenced adaptation time. In the case of sucrose stimulation the inhibitory effect of W-7 is counteracted by the presence of GDPbS. On the other hand, GDPbS affects neither sucrose nor fructose when added to pure sugar solutions. Neither of the two Ca++ chelators had significant effects on the response of the "sugar" cell following stimulation with sucrose, while they lowered fructose stimulating effectiveness.

In this paper we give a good demonstration of the involvement of Ca++ cascade in the sugar reception mechanism even though differences were found between sucrose (which interacts with the "pyranose" site at the membrane level) with respect to fructose (which interacts with the "furanose" site).

References:

1. Green DJ, Gillette R (1988) J Neurophysiol 59:248-258

2. Gödde J, Krefting ER (1989). J Insect Physiol 35: 107-111

3. Hidaka H., Sasaki Y, Tanaka T, Endo T, Ohno S, Fuji Y, Nagata T (1981) Proc Natl Acad Sci USA 78: 4354-4357

4. Hodgson, E. S., Lettvin, JY, Roeder K.D (1955) Science (Washington) 122: 417-418

 


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